This invention relates to heating a dielectric fluid or fluidized particles or particulates and in particular heating an oil and water emulsion or dispersion to facilitate separation thereof.
Water-oil emulsions are almost invariably produced in the extraction of crude oil and are most likely to occur if water flooding is used to maximise recovery of oil from an oil well.
It is desirable to reduce water content of the emulsion to less than 0.5% before the oil is delivered to a refinery. For premium oils a lower concentration of 0.2% water is required. Traditionally, settling tanks are used to allow constituents of an oil and water emulsion or dispersion to separate, possibly using at least one of surfactants and electric precipitators, but this is a time-consuming process and does not maximise recovery.
Thus electrostatic precipitation, which causes water globules to coalesce, is known from, for example, GB 1,155,784 which discloses electrostatic precipitation of water suspended in oil in the presence of synthetic thermoplastic polymers as coalescers, in which the liquid flows through an electric field of from 1 to 60 kV.
GB 1,247,500 discloses a treater for resolving oil-water emulsions containing gas including electrical treatment of emulsions for removal of water in an upward flow. A plurality of vertically disposed screen electrodes may be used with ground electrodes positioned between adjacent pairs of high-voltage electrodes.
GB 1,327,991 discloses a phase separator for immiscible fluids including an outlet separation zone including energized electrodes creating an electric field which enhances coalescence of residual water. Electrodes are supplied from a transformer so apparently an AC field or pulsed field is applied. The electrodes are separated by 4-10 inches (10.2-25.4 cm) and are subjected to 10 kV to 30 kV.
EP 0468954 discloses breaking of oil-in-water or water-in-oil emulsions by subjection to a constant-voltage field to provide a polarisation of the emulsion and an alternating field superimposed on the constant-voltage field.
U.S. Pat. No. 4,257,895 discloses the separation of oil and water from an emulsion in which the emulsion flows vertically through an electric field between two plate electrodes.
U.S. Pat. No. 5,580,464 discloses separation of, for example, a water-in-oil emulsion by introducing bubbles of an electrically insulating gas while applying an electric or electrostatic field across the emulsion, using insulated electrodes. Reference is made to previously known methods of applying a high voltage gradient, AC fields, pulsed AC fields, DC fields and pulsed DC fields. The electric or electrostatic field is applied using one or more pairs of electrodes applying a voltage of 10 to 20 kV pulsed at 1.5 to 50 Hz. The emulsion flows through the electric field. Insulated electrodes are used to apply a pulsed DC field or un-insulated electrodes to apply an AC field.
U.S. Pat. No. 5,865,992 discloses an oil, water and gas separator including an electric field through which the oil can flow downwardly for coalescing water drops entrained within the oil.
US 2001/0017264 discloses a method of separating an insulating liquid from a dispersum, particularly water dispersed in oil, by applying a pulsating electric field of 5-30 kV having a frequency between 60 Hz and 1 kHz dependent on a monitored conductivity of the dispersum. A pulsed DC field of 0.5-5 kV may be applied upstream of the variable frequency field to charge the water droplets and a separating AC field applied downstream of the variable frequency field.
US 2005/0230296 discloses an oil and water separator including downward flow of the oil and water emulsion through an electric field to coalesce entrained water drops for faster gravity separation. The downward flow purges the coalesced water drops from the electric field preventing a high water concentration causing an electrical short circuit.
Emulsions with a relatively low concentration of water, for example less than 25%, take longer to settle out than emulsions with a relatively higher water concentration, because the water globules tend to be smaller and settling is a balance between gravitational and surface tension forces, which are larger in the smaller globules.
If, alternatively, a water-oil emulsion is subjected to microwaves, heat produced by absorption of radiation in the water droplets may be transferred to the oil by conduction, lowering the viscosity of the oil and aiding separation.
U.S. Pat. No. 4,889,639 discloses microwave separation of an emulsion, particularly for enhancing separation of an oil and water emulsion using re-circulating oily water from a separator tank or using water from a separate source. An applicator is provided with an inlet and outlet for passage of an oil-water emulsion or dispersion. Magnets are provided in a microwave circulator located between a microwave source and a waveguide to deflect reflected microwave energy into a water load chamber on the circulator.
U.S. Pat. No. 5,914,014 discloses a microwave applicator to break hydrocarbon and water emulsions. A stream of a hydrocarbon and water emulsion is pumped into a multimode resonant re-entrant microwave cavity. Dual opposing emulsion flow chambers, with a centrally supplied microwave waveguide, form a double ended resonant chamber with multiple RF energy reflections to treat the flowing emulsion. An RF energy applicator reflects energy into the dual opposed RF terminal cavities using angled reflector plates located at a terminal end of a rectangular waveguide. Feedstock flow is upward against gravity to prevent entrained solids from becoming trapped within the resonator cavities. The dual opposed RF terminal cavities act as one multimode resonant re-entrant microwave cavity to absorb microwave energy. The re-entrant chamber dimensions closely match microwave standing wave patterns for predetermined dielectric properties of the oil and water mixture flowing through the dual opposed cavities. A three port circulator is located between a transmitter and the microwave applicator to divert any reflected RF to a water-cooled dummy load. U.S. Pat. Nos. 6,077,400 and 6,086,830 disclose details of feedstock preheating, filtering, and temperature range and details of chamber materials and design for substantially the same apparatus.
U.S. Pat. No. 6,184,427 contemplates recycling waste plastics by treating the waste material with microwaves by passing the waste material through an electric field either generated by a plate capacitor or a ring electrode structure.